This invention relates generally to improvements in methods and apparatus for the measurement of blood pressure and heart rate and, more particularly, to a new and improved electronic sphygmomanometer system enabling very rapid, accurate, reliable and easily obtained blood pressure and heart rate measurements.
It is common practice in the medical arts, as in hospitals and doctors' offices, to employ an auscultation technique for measuring the blood pressure of a patient by using the characteristics of the so-called korotkoff sounds to determine the systolic and diastolic values of the patient's blood pressure.
The korotkoff method typically makes use of an inflatable cuff surrounding a portion of the patient's upper arm. Sufficient inflation of the cuff closes off or completely occludes the brachial artery of the patient. As air is released and the cuff is slowly deflated, a point is reached at which the occluded artery begins to open for a very brief period during each cardiac cycle. At this point, the cuff pressure, which is assumed in using this process as being approximately equal to the blood pressure in the brachial artery, will be that of the peak pressure obtained during the cardiac cycle, this pressure being known in the medical arts as the systolic blood pressure.
Detection of the point at which the artery first opens may be made by any suitable listening device such as a stethoscope or microphone applied to the arm over the artery, usually downstream of the inflated cuff. As the artery opens, auscultatory sounds caused by the pulsating blood flow or turbulence in the blood stream below the occlusion are sensed by the listening device, and these sounds are referred to in the medical arts as the well known korotkoff sounds. At the point of first detection, where the decreasing cuff pressure is matched by the maximum blood pressure, medical personnel skilled in the auscultation technique can detect the pulsatile blood flow in the artery and the onset of korotkoff sounds, and thereby determine the systolic blood pressure.
As the pressure in the cuff continues to drop, the korotkoff sounds continue substantially in synchronization with the blood pressure pulses produced during successive cardiac cycles. Eventually a point is reached at which the artery remains open during the entire cardiac cycle and, at this point, the korotkoff sounds cease entirely. The cuff pressure at this point approximates the lowest blood pressure reached during the cardiac cycle, with the heart essentially at rest, and this is known as the diastolic blood pressure.
Hence, it will be apparent that, if values of the decreasing cuff pressure are correlated with the korotkoff sound output of the stethoscope or microphone, the cuff pressure at the time the first korotkoff sound occurs is approximately equal to the systolic blood pressure, while the cuff pressure at the time the last korotkoff sound occurs is approximately equal to the diastolic blood pressure encountered during the measurement process.
It will be apparent from the foregoing that conventional blood pressure measurement procedures using an inflatable cuff and a suitable listening device are prone to a number of significant deficiencies. In this regard, medical personnel making such measurements are required to make rather difficult determinations regarding the presence or absence of korotkoff sounds which may be of relatively low and difficult to detect amplitudes and are often intermixed and easily confused with ambiguous signals generated by artifacts and both internal and external noise. In this regard, noise and artifact signals generally appear to be produced more frequently in sick patients than in healthy patients so that the process is oftentimes more difficult to perform accurately in those instances where the very requirement for a high degree of accuracy is greatest. In addition, the determination of the end points for the onset and cessation of the korotkoff sound pulse train is somewhat subjective and therefore subject to further inaccuracy in the absence of considerable training and much experience on the part of skilled medical personnel.
Since there are relatively few persons really capable of taking accurate blood pressure measurements using conventional manual auscultation techniques, various attempts have been made in the prior art to eliminate the aforedescribed deficiencies by mechanizing the measurement process so that the subjective factors introduced when an untrained person attempts to measure blood pressures can be eliminated and, further, to provide some discrimination against artifacts and noise. However, such automatic systems for measuring blood pressure and, typically, associated heart rate, have generally proven to be overly sensitive to spurious signals generated by artifacts and noise and have proven, therefore, to be in many instances less accurate than medical personnel using tried and true manual procedures. As a consequence, automatic korotkoff sound monitoring systems for determining blood pressure have experienced only limited acceptance by the medical profession.
Hence, those concerned with the development and use of automatic sphygmomanometers in the medical field have long recognized the need for improved sphygmomanometer systems which enable more accurate and reliable blood pressure and heart rate measurements to be made and which obviate the need for a high degree of skill and subjective expertise on the part of medical personnel making such measurements. The present invention fulfills all of these needs.